(1) Field of the Invention
The present invention relates to a developing process excellent in the image reproducibility. More particularly, the present invention relates to a developing process in which in reproducing multiple fine lines, the width is uniform in the respective lines and so-called front end chipping or rear end chipping is prevented, and a high-quality image can be formed.
(2) Description of the Related Art
A two-component type developer comprising a magnetic carrier and a toner is widely used in commercial electrophotographic copying machines, and in the development of an electrostatically charged image, a magnetic brush of this developer is formed on a developing sleeve having magnetic poles installed therein and the magnetic brush is brought into sliding contact with a photosensitive material having the charged image thereon to form a toner image.
Many proposals have been made in connection with developing conditions adopted for this developing process. For example, Japanese Unexamined Patent Publication No. 59-172660 teaches that a high-density image an excellent gradient can be obtained by using a two-component type developer comprising a ferrite carrier and an electroscopic toner and controlling the toner concentration, the photosensitive drum/developing sleeve peripheral speed ratio and the main pole angle in the developing sleeve within certain ranges. Moreover, Japanese Unexamined Patent Publication No. 61-118767 teaches that in carrying out the development by using a two-component type developer, a uniform high-quality image can be obtained by controlling the surface potential, the D-S distance (the distance between the photosensitive drum and the developing sleeve) and the resistance value of the magnetic carrier within certain ranges.
Furthermore, Japanese Unexamined Patent Publication No. 63-208867 teaches that in the developing process using a two-component developer comprising a magnetic carrier and a toner, scattering of the image density can be prevented by adjusting the packing ratio (PD) of the developer, defined by the following formula, to 20 to 50%: EQU PD=M/(.rho..times.Ds).times.100
wherein M represents the amount of the developer which has passed through the portion for regulating the height of the magnetic brush on the developing sleeve, .rho. represents the true specific gravity (g/cm.sup.3) of the developer, and Ds represents the distance between the developing sleeve and the electrostatic latent image recording material.
In each of the former two proposals, the characteristics of the developer and the developing conditions are independently defined, and the practical developing operation is not comprehensively grasped. Furthermore, the characteristics of the developer and carrier are not defined by the dynamic state of an actual machine but under static conditions. Accordingly, the process does not cope effectively with the actual developing operation in a copying machine.
It is deemed that the latter proposal is significant in that attention is paid to the packing ratio of the developer in the developing zone. However, the contact state between the magnetic brush of the developer and the surface of the photosensitive material under actual developing conditions, that is, dynamic conditions, is not defined, and the process does not cope effectively with the actual developing operation.